1. Field of the Invention
The present invention relates to an optical component and a method for producing the optical component.
2. Description of Related Art
Glass lenses to be used for DSC (digital still camera) or DVC (digital video camera) are produced by press forming. Glass lenses having an aspherical shape can be produced at low cost by press forming.
In order to produce lenses with high shape accuracy, it is important to prevent glass from fusion bonding to a forming die, and the forming die is required to have very high surface accuracy and low surface roughness, in press forming. The following techniques are proposed for improving the glass (formed lens) separation from a forming die. JP 62 (1987)-207728 A discloses a technique in which the surface of a glass substrate is provided with a surface layer having a lower concentration of easily volatile components than the glass main body so that high surface accuracy and low surface roughness of a forming die can be ensured. JP 8 (1996)-217468 A discloses a technique for preventing glass from fusion bonding to a forming die by forming a carbon film on the surface of a glass preform.
It should be noted that the term “fusion bonding” in this description means a phenomenon in which a part of glass adheres to a forming die so as to remain as a residue on the surface of the forming die, or a phenomenon in which the formed product (lens) of glass sticks to the forming die. In forming a thin lens, either phenomenon can occur.
In recent years, the demand for reduction in size of image pickup optical systems represented by DSC and DVC has been increasing more and more. In order to reduce the size of image pickup optical systems, it is necessary to reduce the lens thickness. Specifically, it is necessary to establish a technique for mass producing very thin lenses such as concave lenses having a thickness of 0.5 mm or less in its center portion and a convex lens having a thickness of 0.5 mm or less in its outer peripheral portion (edge portion).
However, it is very difficult to produce such a thin lens by conventional press forming methods. In forming a lens, load is concentrated on the thin portion of the lens, thus causing glass to be fusion bonded to a forming die notably. The fusion bonding of glass to the forming die not only deteriorates the shape accuracy of a lens as a finished product, but also impairs the surface accuracy of the forming die because of the residual glass adhering to the forming die, which makes it difficult to use the same forming die continuously. Although the techniques disclosed in JP 62 (1987)-207728 A and JP 8 (1996)-217468 A have some effect in preventing the glass from fusion bonding to the forming die, the effect is still insufficient. Further, the techniques of JP 62 (1987)-207728 A and JP 8 (1996)-217468 A suffer from problems such as an increase in the number of steps, and an increase in cost, because various pretreatments are required therein.